In order to understand physical and chemical processes on material surfaces, such as catalysts, semiconductors, sensors and electronic devices, and develop highly functional materials, atomic-level elemental analysis and chemical state analysis of the surface of such materials are required. The invention of scanning tunneling microscope (STM) in 1982 achieved the observation of the conductive material surfaces and another invention of non-contact atomic force microscope (NC-AFM) in 1995 accomplished the observation of the insulating material surfaces at the atomic level. In addition to surface structure observation, the atomic force microscope is widely used for identifying various physical properties of materials, such as magnetic, electrical and mechanical properties, and functions like the extent of mechanical contact force and surface force for a minute.
However, microscope images obtained by the above conventional microscopes essentially involve no direct elemental or chemical state information on a observed material surface.
Meanwhile, to obtain atomic-level elemental or chemical state information of a solid surface, the following conventionally-known approaches are mainly suggested: (1) optical illumination scanning tunneling microscopy combined with visible light, (2) inelastic electron tunneling spectroscopy based on inelastic effect in tunneling process and (3) radiation-light exciting scanning tunneling microscopy combined with radiant X-ray.
Nevertheless, in the approaches of (1) and (3), practical use is not achieved despite their continued development, while the approach of (2) is characterized by the measurement of molecules attached to the solid surface, rather than the analysis of the solid surface itself.
On the other hand, a conventional non-contact atomic force microscope, as disclosed in Japanese Unexamined Patent Publication No. 2000-028511, comprises a cantilever secured to an oscillating means, a displacement detector for detecting the displacement of the cantilever, an amplifier for controlling said oscillating means, a frequency detector for detecting the output frequency of said displacement detector, a sample driving means for changing the distance between the sample and the distal end of the cantilever so as to keep the frequency detected constant and a control apparatus for each driving oscillating means with distinct oscillating voltages caused by controlling said amplifier. The control apparatus detects the change in oscillating frequency corresponding to the change in distance between the sample and the distal end of the cantilever at each oscillating voltage from the output of said frequency detector, and determines the oscillation amplitude of the cantilever from the difference between sudden rising positions of said oscillating frequency at each oscillating voltage.
Patent Document 1: Japanese Unexamined Patent Publication No. 2000-28511